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Date:   Wed, 25 Oct 2017 11:24:28 +0200
From:   Mark Brown <broonie@...nel.org>
To:     Igor Plyatov <plyatov@...il.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Cyrille Pitchen <cyrille.pitchen@...rochip.com>,
        Ludovic Desroches <ludovic.desroches@...el.com>
Cc:     linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mmc@...r.kernel.org, Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: spi-atmel.c: regression

On Thu, Oct 05, 2017 at 10:05:57AM +0300, Igor Plyatov wrote:

> > please help to manage issue with data corruption by PDC of SPI.
> > 
> > 
> > I have compared operation of Linux-2.6.39 and linux4sam kernel 4.9.36+
> > on the AT91SAM9G20 (Stamp9G20 SOM from Taskit.de) and found regression
> > in the spi-atmel.c.

Nobody working on the driver has any thoughts on this?

> > 
> > New spi-atmel.c driver works very bad with SPI speeds above 6 MHz. I see
> > corruption in data received by Linux and SPI overruns when OS has big
> > CPI and IO load.
> > 
> > Old kernel works fine at 22 MHz with the same device driver and hardware.
> > 
> > Can somebody comment and/or help on how to resolve this issue?
> > 
> > Best wishes.
> > -- 
> > Igor Plyatov
> 
> For those, who has same interest or encountered the same issue as I had...
> 
> Notes:
> A) My "gs_mgms_dsp" linux driver is the same for linux-2.6.39 and
> linux-4.9.36
>    and communicates with DSP through SPI-bus, where data packets are 32 byte
>    long and last byte is CRC8 to check data integrity.
> B) CPU is AT91SAM9G20.
> 
> I have encoutered SPI data corruption during receiving of data from DSP by
> linux-4.9.36 if SPI-bus has big traffic in parallel with big traffic at MMC
> interface.
> 
> Old linux-2.6.39 does not suffer from such issue, because atmel-mci.c driver
> has
> PIO access to MMC interface. While new kernel has changed the atmel-mci.c
> driver
> for use of PDC (Peripheral DMA Controller) for access to MMC interface.
> 
> Both kernels have Atmel SPI driver where PDC used for SPI data transfers.
> 
> SPI data corruption looks like duplication of one of received bytes.
> Such bytes surrounded by "**" at log below.
> 
> gs_mgms_dsp spi32766.0: CRC error.
> gs_mgms_dsp spi32766.0: <- 35 36 37 38 39 3A 3B 3C 3D  3E 3F  40 41 42 43 44
> gs_mgms_dsp spi32766.0: <- 45 46 47 48 49 4A 4B 4C 4D *4F 4F* 50 51 52 53 A4
> gs_mgms_dsp spi32766.0: -> EIO=0x05
> gs_mgms_dsp spi32766.0: CRC error.
> gs_mgms_dsp spi32766.0: <- 0F C2 C3 C4 C5 C6 C7 C8 C9  CA CB  CC CD CE CF D0
> gs_mgms_dsp spi32766.0: <- D1 D2 D3 D4 D5 D6 D7 D8 D9 *DB DB* DC DD DE DF 02
> gs_mgms_dsp spi32766.0: -> EIO=0x05
> gs_mgms_dsp spi32766.0: CRC error.
> gs_mgms_dsp spi32766.0: <-  03 5A  5B 5C 5D 5E 5F 60 61 62 63 64 65 66 67 68
> gs_mgms_dsp spi32766.0: <- *6A 6A* 6B 6C 6D 6E 6F 70 71 72 73 74 75 76 77 25
> gs_mgms_dsp spi32766.0: -> EIO=0x05
> gs_mgms_dsp spi32766.0: CRC error.
> gs_mgms_dsp spi32766.0: <- 15 76 77 78 79 7A  7B 7C  7D 7E 7F 80 81 82 83 84
> gs_mgms_dsp spi32766.0: <- 85 86 87 88 89 8A *8C 8C* 8D 8E 8F 90 91 92 93 00
> gs_mgms_dsp spi32766.0: -> EIO=0x05
> gs_mgms_dsp spi32766.0: CRC error.
> gs_mgms_dsp spi32766.0: <- 2A EC ED EE EF F0 F1  F2 F3  F4 F5 F6 F7 F8 F9 FA
> gs_mgms_dsp spi32766.0: <- FB FC FD FE FF 00 01 *03 03* 04 05 06 07 08 09 0A
> gs_mgms_dsp spi32766.0: -> EIO=0x05
> 
> This looks like silent SPI overruns not detected by AT91SAM9G20 HW.
> 
> At the end, after some seconds or milliseconds of communication, HW SPI
> overrun
> flag detected by the spi-atmel.c driver:
> "atmel_spi fffcc000.spi: overrun (0/0 remaining)".
> 
> Strictly speaking this is not a regression of spi-atmel.c, but unfortunate
> combination with atmel-mmc.c, where PDC used too and I suppose a HW bug in
> AT91SAM9G20 CPU.
> 
> Please help to answer on questions:
>   1) How to modify atmel-mci.c driver to have option for PIO access to MMC
>      interface?
>   2) Why SPI overrun flag does not asserted each time? I have not found such
> HW bug
>      in the Errata for AT91SAM9G20 CPU.
> 
> Best wishes.
> --
> Igor Plyatov

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